1. Technical Field
The present invention relates to control systems and methods, as well as, communication devices and methods, and in particular, to a control system and method, as well as, a communication device and method that suppress occurrence of collision and enable communication to be carried out more efficiently and accurately.
2. Related Art
A system that controls locking and unlocking of the door, for example, based on a signal transmitted from a portable device having a wireless communication function is conventionally known. For example, there is known a control system that receives a signal transmitted from a portable device having a wireless communication function by an in-vehicle wireless device mounted on an automobile, authenticates identification information of the portable device contained in the signal, and performs a predetermined process such as locking and unlocking of the door of the automobile or startup of the engine of the automobile when the authentication is successful.
With such a control system, there can be realized a so-called passive entry/passive start of locking and unlocking the door of the automobile or startup of the engine of the automobile without requiring an operation of, for example, inserting a key to a key hole and turning the key as in prior art. Specifically, the user can easily lock and unlock the door of the automobile or start up the engine of the automobile by simply operating a door knob or an engine start button of the automobile with the portable device positioned within a communicable range of the in-vehicle wireless device (in a normal case, the state in which the portable device is simply carried around).
In such a control system, the portable device transmits a response signal with respect to a request signal to the in-vehicle wireless device when receiving the request signal from the in-vehicle wireless device to indicate that it is positioned within the communicable range of the in-vehicle wireless device. However, if a plurality of portable devices exists within the communicable range of the in-vehicle wireless device, each of portable devices transmits the response signal with respect to the request signal at the same timing, whereby collision occurs among the response signals, and the in-vehicle wireless device may not be able to correctly receive such response signals.
A method is considered in which the in-vehicle wireless device retransmits the request signal, which individually specifies the portable device, to the portable device at different timing from each other when collision of the response signals occurred (see e.g., Japanese Unexamined Patent Publication Nos. 2008-150835 and 2008-150836).
In this method, the in-vehicle wireless device transmits the request signal for the portable device at different timing from each other with the identification information of the portable device contained in the request signal when a predetermined instructing operation such as unlocking, locking, or engine startup is performed by the user. The timing at which the portable device receives the request signal with respect to each other is differed from each other by shifting the transmission timing of the request signal. The occurrence of collision of the response signals is suppressed since the transmission timing of the response signal of the portable device also differs from each other.